Papers by Alfonso López Martínez
Ingeniería Energética, Apr 1, 2019
Licencia de uso y distribución Creative Commons Reconocimiento-No Comercial 4.0 Internacional.
The wideband regime of bit-interleaved coded modulation (BICM) in Gaussian channels is studied. T... more The wideband regime of bit-interleaved coded modulation (BICM) in Gaussian channels is studied. The Taylor expansion of the coded modulation capacity for generic signal constellations at low signal-tonoise ratio (SNR) is derived and used to determine the corresponding expansion for the BICM capacity. Simple formulas for the minimum energy per bit and the wideband slope are given. BICM is found to be suboptimal in the sense that its minimum energy per bit can be larger than the corresponding value for coded modulation schemes. The minimum energy per bit using standard Gray mapping on M-PAM or M 2-QAM is given by a simple formula and shown to approach-0.34 dB as M increases. Using the low SNR expansion, a general trade-off between power and bandwidth in the wideband regime is used to show how a power loss can be traded off against a bandwidth gain.
In this letter we determine the derivative of the mutual info rmation corresponding to bit-interl... more In this letter we determine the derivative of the mutual info rmation corresponding to bit-interleaved coded modulation systems. The derivative follows as a linea r combination of minimum-mean-squared error functions of coded modulation sets. The result finds ap plications to the analysis of communications systems in the wideband regime and to the design of power allo cation over parallel channels.
This dissertation studies a new family of channel models for non-coherent com- munications, the a... more This dissertation studies a new family of channel models for non-coherent com- munications, the additive energy channels. By construction, the additive en- ergy channels occupy an intermediate region between two widely used channel models: the discrete-time Gaussian channel, used to represent coherent com- munication systems operating at radio and microwave frequencies, and the discrete-time Poisson channel, which often appears in the analysis of intensity- modulated systems working at optical frequencies. The additive energy chan- nels share with the Gaussian channel the additivity between a useful signal and a noise component. However, the signal and noise components are not complex- valued quadrature amplitudes but, as in the Poisson channel, non-negative real numbers, the energy or squared modulus of the complex amplitude. The additive energy channels come in two variants, depending on whether the channel output is discrete or continuous. In the former case, the energy is a mult...
2006 Conference on Lasers and Electro-Optics and 2006 Quantum Electronics and Laser Science Conference, 2006
Revista Colombiana De Psicologia, Sep 24, 2012
IEE Seminar on Optical Fibre Communications and Electronic Signal Processing, 2005
Revista de Metalurgia, 1998
Resumen Se ha construido un método sencillo y rápido para evaluar la eficiencia y condiciones de ... more Resumen Se ha construido un método sencillo y rápido para evaluar la eficiencia y condiciones de estabilidad en los procesos de conformado de materiales metálicos. Se parte de la resolución de la ecuación de Garofalo para la fluencia plástica en estado estacionario. Utilizando los parámetros de ajuste de la mencionada ecuación y de acuerdo con el significado físico de los mismos, se desarrollan las herramientas numéricas necesarias para obtener los mapas energéticos de eficiencia del tratamiento, así como las condiciones más aconsejables para el conformado del material. Además, se obtienen mapas de parámetros cuyo significado físico posee interés intrínseco, como valores de energías de activación efectivas para zonas concretas del tratamiento de los materiales y un procedimiento para obtener a partir del valor del exponente {n G } de la ecuación de Garofalo, los exponentes {n PL }, característicos de las leyes potencias para intervalos reducidos de las variables de trabajo. Palabras clave: Mapas de procesado. Conformado en caliente. Técnicas de modelización. A model for construction of efficiency and stability maps of hot working processes in polycrystalline metallic materials using the Garofalo's equation Abstract Has been developed a fast and easy method for to evalúate the efficiency of the process and some of posible stabilities situations in the hot workin process for the pollicrystalines metalics materials (p.m.m.), by the obtained dates in the Garofalo's equation resolution for the steady state creep and for wide ranges of the work variables, stress, strain rate and temperature. These method use the fitting parameters obtained for the equation mentioned and of their physical meaning. Has been developed the numerical treatment from our previously developed "software" for the analysis of "creep", and we can obtained the efficiency energetic maps for the "creep" and the more generaly advises áreas for the hot working. Further more has been obtained maps for parameters of great physical significance; f.e. the effective activation energy for differents áreas of the materials hot working, and in addittion has been developed a method for obtained the valúes of {n PL } for the differents ranges of "power-law" aplication, when has been obtained the valué of {n G } in the Garofalo's equation.
31st European Conference on Optical Communications (ECOC 2005), 2005
Revista de Metalurgia, 1998
Resumen Se describe el uso y explotación de un algoritmo integrado para el ajuste de la ecuación ... more Resumen Se describe el uso y explotación de un algoritmo integrado para el ajuste de la ecuación de Garofalo a los resultados de ensayos experimentales de torsión y de tracción, y su capacidad de predecir valores para las variables de conformado, fuera de los rangos de trabajo de los ensayos; se analiza la verosimilitud del ajuste y de las predicciones realizadas. Se ha aplicado el método a los resultados de ensayos de torsión y de tracción para la aleación TÍ-6A1-4V. Palabras clave: Ecuación de Garofalo. Predicción de fluencia. Deformación plástica. Análisis numérico. Análisis estadístico.
2006 IEEE International Symposium on Information Theory, 2006
This paper investigates the transmission of information by placing balls in urns. Alice, the tran... more This paper investigates the transmission of information by placing balls in urns. Alice, the transmitter, encodes her message in her choice of the number of balls at each urn, which follows a Poisson distribution, and is subject to an average constraint. Two adversaries, Marvin and Charlie, also put balls into the urns, respectively with geometric and Poisson distributions. Bob, the receiver, retrieves the message by counting the balls in all urns. We provide upper and lower bounds to the channel capacity. We further illustrate the links between this model and electromagnetic radiation, by replacing balls by photons and urns by frequencies or colours.
2014 8th International Symposium on Turbo Codes and Iterative Information Processing (ISTC), 2014
A source-channel coding scheme in which source messages are assigned to two classes and encoded u... more A source-channel coding scheme in which source messages are assigned to two classes and encoded using a channel code that depends on the class index is studied. A lowcomplexity implementation with two quasi-cyclic LDPC codes with belief-propagation decoding achieves a better frame error rate than optimized separate coding. The coding gain obtained by simulation is consistent with the theoretical gain.
Optics Letters, 2012
We provide, to our knowledge, the first experimental demonstration of the feasibility of sending ... more We provide, to our knowledge, the first experimental demonstration of the feasibility of sending several parallel keys by exploiting the technique of subcarrier multiplexing (SCM) widely employed in microwave photonics. This approach brings several advantages such as high spectral efficiency compatible with the actual secure key rates, the sharing of the optical fainted pulse by all the quantum multiplexed channels reducing the system complexity, and the possibility of upgrading with wavelength division multiplexing in a two-tier scheme, to increase the number of parallel keys. Two independent quantum SCM channels featuring a sifted key rate of 10 Kb∕s∕channel over a link with quantum bit error rate <2% is reported.
International Journal of Satellite Communications and Networking, 2006
This paper investigates the design of power and spectrally efficient coded modulations based on A... more This paper investigates the design of power and spectrally efficient coded modulations based on Amplitude Phase Shift Keying (APSK) modulation with application to satellite broadband communications. APSK represents an attractive modulation format for digital transmission over nonlinear satellite channels due to its power and spectral efficiency combined with its inherent robustness against nonlinear distortion. For these reasons APSK has been very recently introduced in the new standard for satellite Digital Video Broadcasting named DVB-S2 [1]. Assuming an ideal rectangular transmission pulse, for which no nonlinear inter-symbol interference is present and perfect pre-compensation of the nonlinearity, we optimize the APSK constellation. In addition to the minimum distance criterion, we introduce a new optimization based on channel capacity; this new method generates an optimum constellation for each spectral efficiency. To achieve power efficiency jointly with low bit error rate (BER) floor we adopt a powerful binary serially concatenated turbo-code coupled with optimal APSK modulations through bit-interleaved coded modulation. We derive tight approximations on the maximumlikelihood decoding error probability, and results are compared with computer simulations. In Ref. [2], the current analysis is complemented with the effects related to satellite nonlinear distortion effects with a band-limited transmission pulse and including demodulator timing,
IEEE Transactions on Wireless Communications, 2006
IEEE Transactions on Information Theory, 2006
This correspondence presents a simple method to accurately compute the error probability of bit-i... more This correspondence presents a simple method to accurately compute the error probability of bit-interleaved coded modulation (BICM). Thanks to the binary-input output-symmetric (BIOS) nature of the channel, the pairwise error probability (PEP) is equal to the tail probability of a sum of random variables with a particular distribution. This probability is in turn computed with a saddlepoint approximation. Its precision is numerically validated for coded transmission over standard Gaussian noise and fully interleaved fading channels for both convolutional and turbo-like codes. Index Terms-Additive white Gaussian noise (AWGN) channel, bit-interleaved coded modulation (BICM), error probability, saddlepoint approximation, Gaussian approximation, fading channel.
IEEE Transactions on Information Theory, 2011
IEEE Transactions on Information Theory, 2010
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Papers by Alfonso López Martínez